U.S. patent number 8,573,196 [Application Number 12/850,862] was granted by the patent office on 2013-11-05 for startup/shutdown systems and methods for a solar thermal power generating facility.
This patent grant is currently assigned to Babcock Power Services, Inc.. The grantee listed for this patent is Leon Afremov, Craig Gillum, Gabriel Kaufmann, Robert Kunkel, Yona Magen, Andrew Plotkin, Kevin Toupin. Invention is credited to Leon Afremov, Craig Gillum, Gabriel Kaufmann, Robert Kunkel, Yona Magen, Andrew Plotkin, Kevin Toupin.
United States Patent |
8,573,196 |
Plotkin , et al. |
November 5, 2013 |
Startup/shutdown systems and methods for a solar thermal power
generating facility
Abstract
A startup system for a solar boiler includes a main fluid
circuit having a plurality of solar boiler panels for generating
power from solar energy. An auxiliary fluid circuit is selectively
connected in fluid communication with the main fluid circuit by a
plurality of valves. An auxiliary boiler is operatively connected
to the auxiliary fluid circuit. The valves connecting the auxiliary
fluid circuit to the main fluid circuit are configured to be opened
and closed to selectively place the auxiliary boiler in fluid
communication with portions of the main fluid circuit to supply
heat to the portions of the main fluid circuit in preparation to
produce power from solar energy.
Inventors: |
Plotkin; Andrew (Worcester,
MA), Gillum; Craig (West Boylston, MA), Toupin; Kevin
(Princeton, MA), Kunkel; Robert (Leominster, MA),
Kaufmann; Gabriel (Beit Hananya, IL), Afremov;
Leon (Yehud, IL), Magen; Yona (Brookline,
MA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Plotkin; Andrew
Gillum; Craig
Toupin; Kevin
Kunkel; Robert
Kaufmann; Gabriel
Afremov; Leon
Magen; Yona |
Worcester
West Boylston
Princeton
Leominster
Beit Hananya
Yehud
Brookline |
MA
MA
MA
MA
N/A
N/A
MA |
US
US
US
US
IL
IL
US |
|
|
Assignee: |
Babcock Power Services, Inc.
(Worcester, MA)
|
Family
ID: |
45555154 |
Appl.
No.: |
12/850,862 |
Filed: |
August 5, 2010 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20120031395 A1 |
Feb 9, 2012 |
|
Current U.S.
Class: |
126/609; 126/640;
60/641.15; 126/646; 60/641.8 |
Current CPC
Class: |
F03G
6/003 (20130101); F03G 6/00 (20130101); F24S
10/00 (20180501); F24S 20/20 (20180501); F03G
7/04 (20130101); F24S 80/00 (20180501); Y02E
10/46 (20130101); Y02E 10/44 (20130101); Y02T
10/7072 (20130101) |
Current International
Class: |
F24J
2/42 (20060101); F24J 2/04 (20060101); B60K
16/00 (20060101); F03G 6/00 (20060101) |
Field of
Search: |
;126/609,615,640,646,572-575,601-602 ;60/641.8,641.15 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2711291 |
|
Dec 1977 |
|
DE |
|
2501839 |
|
Sep 1982 |
|
FR |
|
53131309 |
|
Nov 1978 |
|
JP |
|
08326223 |
|
Dec 1996 |
|
JP |
|
WO-2008154599 |
|
Dec 2008 |
|
WO |
|
Other References
Derwent Abstract: DE 2711291. cited by examiner .
PCT International Search Report and Written Opinion dated Aug. 4,
2011 issued on corresponding International patent application No.
PCT/US2011/046644. cited by applicant .
U.S. Appl. No. 60/943,096, Kroizer. cited by applicant .
International Search Report and Written Opinion, dated Aug. 30,
2010 for PCT/US2010/023124. cited by applicant .
International Search Report and Written Opinion, dated Aug. 31,
2010 for PCT/US2010/023165. cited by applicant .
International Search Report and Written Opinion, dated Oct. 13,
2010 for PCT/US2010/023622. cited by applicant .
International Search Report and Written Opinion, dated Oct. 13,
2010 for PCT/US2010/023826. cited by applicant .
International Search Report and Written Opinion, dated Dec. 13,
2010 for PCT/US2010/023367. cited by applicant .
International Search Report and Written Opinion, dated Dec. 13,
2010 for PCT/US2010/023500. cited by applicant.
|
Primary Examiner: Rinehart; Kenneth
Assistant Examiner: Sullens; Tavia
Attorney, Agent or Firm: Edwards Wildman Palmer LLP Neuner;
George W. Jones; Joshua L.
Claims
What is claimed is:
1. A method of starting up a solar boiler comprising: a)
circulating fluids heated by an auxiliary boiler through an
auxiliary fluid circuit that includes a plurality of superheater
panels to elevate temperatures within the superheater panels; b)
circulating fluids through a plurality of steam generator panels
exposed to solar radiation to elevate temperatures within the steam
generator panels; and c) supplying steam from the steam generator
panels to the superheater panels to bring a drum and superheater
panels up to an operational temperature for producing solar power
by: i) connecting the drum to the steam generator panels; ii)
connecting the drum to the superheater panels by opening a drum
isolation valve connected between the drum and the superheater
panels; and iii) disconnecting the auxiliary boiler from the
superheater panels by closing an auxiliary boiler bypass valve
connected between the superheater panels and the auxiliary boiler;
and d) timing the step of connecting the drum to the steam
generator panels to occur after local sunrise, wherein the step of
connecting the drum to the superheater panels includes heating the
superheater panels with solar heat flux.
2. A method as recited in claim 1, wherein the step of connecting
the drum to the superheater panels includes connecting a plurality
of reheater panels in series between the superheater panels and a
condenser to bring the superheater panels and the reheater panels
up to an operational temperature for producing solar power.
3. A method as recited in claim 2, further comprising connecting a
first turbine stage in series between the superheater panels and
the reheater panels by opening a first turbine valve connected
between the superheater panels and the first turbine stage and
closing a first turbine bypass valve connected between the
superheater panels and the reheater panels, and connecting a second
turbine stage in series between the reheater panels and the
condenser by opening a second turbine valve connected between the
reheater panels and the second turbine stage and closing a second
turbine bypass valve connected between the reheater panels and the
condenser.
4. A method as recited in claim 1, wherein the step of circulating
fluids through a plurality of steam generator panels exposed to
solar radiation to elevate temperatures within the steam generator
panels includes heating fluids within the steam generator panels to
a temperature within about .+-.100.degree. F. of that within the
drum.
5. A method as recited in claim 4, further comprising initiating
the step of circulating fluids heated by an auxiliary boiler
through an auxiliary fluid circuit prior to local sunrise.
6. A method of starting up a solar boiler comprising: a)
circulating fluids heated by an auxiliary boiler through an
auxiliary fluid circuit that includes a plurality of superheater
panels to elevate temperatures within the superheater panels; b)
circulating fluids through a plurality of steam generator panels
exposed to solar radiation to elevate temperatures within the steam
generator panels; and c) supplying steam from the steam generator
panels to the superheater panels to bring a drum and superheater
panels up to an operational temperature for producing solar power
by: i) connecting the drum to the steam generator panels; ii)
connecting the drum to the superheater panels by opening a drum
isolation valve connected between the drum and the superheater
panels; and iii) disconnecting the auxiliary boiler from the
superheater panels by closing an auxiliary boiler bypass valve
connected between the superheater panels and the auxiliary boiler;
and d) initiating the step of connecting the drum to the
superheater panels after local sunrise.
7. A method as recited in claim 6, wherein the step of connecting
the drum to the superheater panels includes connecting a plurality
of reheater panels in series between the superheater panels and a
condenser to bring the superheater panels and the reheater panels
up to an operational temperature for producing solar power.
8. A method as recited in claim 7, further comprising connecting a
first turbine stage in series between the superheater panels and
the reheater panels by opening a first turbine valve connected
between the superheater panels and the first turbine stage and
closing a first turbine bypass valve connected between the
superheater panels and the reheater panels, and connecting a second
turbine stage in series between the reheater panels and the
condenser by opening a second turbine valve connected between the
reheater panels and the second turbine stage and closing a second
turbine bypass valve connected between the reheater panels and the
condenser.
9. A method as recited in claim 6, wherein the step of circulating
fluids through a plurality of steam generator panels exposed to
solar radiation to elevate temperatures within the steam generator
panels includes heating fluids within the steam generator panels to
a temperature within about .+-.100.degree. F. of that within the
drum.
10. A method as recited in claim 9, further comprising initiating
the step of circulating fluids heated by an auxiliary boiler
through an auxiliary fluid circuit prior to local sunrise.
11. A method of shutting down a solar boiler to enable subsequent
rapid startup comprising: a) cooling fluids in a main fluid circuit
of a solar boiler to a temperature below operational temperature
for power production, wherein the main fluid circuit includes a
plurality of solar boiler panels and a drum; b) isolating the drum
from the solar boiler panels by closing at least one drum isolation
valve in the main fluid circuit, wherein the drum is insulated to
preserve heat therein when isolated from the solar boiler panels
wherein the step of cooling includes cooling fluids in the drum to
a temperature within .+-.200.degree. F. of maximum operating
temperature of an auxiliary boiler operatively connected to the
main fluid circuit to be brought selectively into fluid
communication therewith to heat portions of the main fluid circuit
during startup; and c) initiating the step of cooling prior to
local sunset.
12. A method as recited in claim 11, wherein the step of isolating
the drum includes cooling fluids in the solar boiler panels to
around ambient temperature.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to solar power production, and more
particularly to systems and methods of power production with solar
boilers.
2. Description of Related Art
Solar power generation has been considered a viable source to help
provide for energy needs in a time of increasing consciousness of
the environmental aspects of power production. Solar energy
production relies mainly on the ability to collect and convert
energy freely available from the sun and can be produced with very
little impact on the environment. Solar power can be produced
without creating radioactive waste as in nuclear power production,
and without producing pollutant emissions including greenhouse
gases as in fossil fuel power production. Solar power production is
independent of fluctuating fuel costs and does not consume
non-renewable resources.
Solar power generators generally employ fields of controlled
mirrors, called heliostats, to gather and concentrate sunlight on a
receiver to provide a heat source for power production. A solar
receiver typically takes the form of a panel of tubes conveying a
working fluid therethrough. Previous solar generators have used
working fluids such as molten salt because it has the ability to
store energy, allowing power generation when there is little or no
solar radiation, such as at night time. The heated working fluids
are typically conveyed to a heat exchanger where they release heat
into a second working fluid such as air, water, or steam. Power is
generated by driving heated air or steam through a turbine that
drives an electrical generator.
More recently, it has been determined that solar production can be
increased and simplified by using water/steam as the only working
fluid in a receiver that is a boiler. This can eliminate the need
for an inefficient heat exchanger between two different working
fluids. This development has lead to new challenges in handling the
intense solar heat without damage to the system. In a solar boiler,
heat transfer rates can reach levels around 2-3 times the heat
transfer rate of a typical fossil fuel fired boiler. This high heat
transfer rate intensifies problems related to maintaining even
heating and flow distribution throughout known designs of boiler
panels. If flow through a portion of a receiver panel is
insufficient when using water/steam as a working fluid, overheating
can result for that panel portion. Such overheating can result in
damage or failure of the panel and its constituent tubes if the
temperatures are allowed to become severe.
Another way in which solar boilers differ from fossil fuel fired
boilers is in terms of operating hours. Fossil fuel fired boilers
typically operate continuously, stopping only for occasional
routine maintenance, whereas solar boilers must start up and shut
down once per day due to the rising and setting of the sun. Any
working fluid and boiler components that cool down during the
overnight layover must be brought back up to operating temperature
each morning. There results a daily thermal expansion cycle that
can result in increased fatigue failure in typical boiler
components.
Traditional boiler designs use considerable time in starting up and
shutting down. Since solar power is only available during daylight
hours each day, these lengthy start up and shut down cycles can
deprive the system of valuable operating hours that could otherwise
be used for power production. One reason for the lengthy start up
and shut down times is the difference in day time operating
temperature and layover temperature at night, which can reach
freezing temperatures. For example, starting a traditional boiler
system too rapidly under these conditions can exacerbate the
thermal expansion issues described above. On the other hand,
starting a traditional boiler system too slowly can result in a
failure to adequately circulate fluids through the boiler tubes,
which can lead to boiler tube failure under the intense heat
flux.
Such conventional methods and systems have generally been
considered satisfactory for their intended purpose. However, there
is still an need in the art for systems and methods that allow for
improved startup and shut down of solar boilers. There also remains
a need in the art for such systems and methods that are easy to
make and use. The present invention provides a solution for these
problems.
SUMMARY OF THE INVENTION
The subject invention is directed to a new and useful startup
system for a solar boiler. The system includes a main fluid circuit
having a plurality of solar boiler panels for generating power from
solar energy. An auxiliary fluid circuit is selectively connected
in fluid communication with the main fluid circuit by a plurality
of valves. An auxiliary boiler is operatively connected to the
auxiliary fluid circuit. The valves connecting the auxiliary fluid
circuit to the main fluid circuit are configured to be opened and
closed to selectively place the auxiliary boiler in fluid
communication with portions of the main fluid circuit to supply
heat to the portions of the main fluid circuit in preparation to
produce power from solar energy.
In accordance with certain embodiments, the auxiliary boiler is a
fuel fired boiler. Any suitable type of boiler can also be used,
including, for example, liquid fuel fired, coal fired, biomass
fired, natural gas fired, nuclear, geothermal, and electric. It is
contemplated that the main fluid circuit can include a drum for
separating steam from liquid water. The plurality of solar boiler
panels can include a plurality of steam generator panels, a
plurality of superheater panels, and a plurality of reheater panels
each configured to transfer solar energy into the main fluid
circuit. The drum can be operatively connected to the steam
generator panels to receive saturated water-steam therefrom, and
operatively connected to supply steam to the superheater
panels.
In certain embodiments, a drum isolation valve is operatively
connected to the main fluid circuit to selectively isolate the drum
from other portions of the main fluid circuit to preserve thermal
energy within the drum during inactive periods of the solar boiler
panels. The drum can be insulated to preserve heat therein during
layover periods with the solar boiler panels inactive.
The system can include a steam generator isolation valve in the
main fluid circuit in an outlet of the drum. In an open state, the
steam generator isolation valve connects the steam generator panels
to the drum to heat the steam generator panels to a temperature
around that of the drum using heat from solar energy. The plurality
of valves connecting the auxiliary fluid circuit to the main fluid
circuit can include a superheater isolation valve that in an open
state connects the auxiliary fluid circuit to a portion of the main
fluid circuit that includes the superheater and reheater panels for
building temperatures therein for full solar operation in the main
fluid circuit.
In accordance with certain embodiments, a first turbine bypass
valve in an open state connects the superheater panels in direct
series with the reheater panels, and a second turbine bypass valve
in an open state connects the reheater panels to a condenser in the
main fluid circuit in preparation for full solar operation. It is
also contemplated that in certain embodiments a first turbine valve
in an open state connects a first turbine stage in series between
the superheater panels and the reheater panels with the first
turbine bypass valve closed, and a second turbine valve in an open
state connects a second turbine stage in series between the
reheater panels and the condenser with the second turbine bypass
valve closed.
The invention also provides a method of starting up a solar boiler.
The method includes circulating fluids heated by an auxiliary
boiler through an auxiliary fluid circuit that includes a plurality
of superheater panels to elevate temperatures within the
superheater panels. Fluids are circulated through a plurality of
steam generator panels exposed to solar radiation to elevate
temperatures within the steam generator panels. The method also
includes supplying steam from the steam generator panels to the
superheater panels to bring the drum and superheater panels up to
an operational temperature for producing solar power by connecting
the drum to the steam generator panels, connecting a drum to the
superheater panels by opening a drum isolation valve connected
between the drum and the superheater panels, and disconnecting the
auxiliary boiler from the superheater panels by closing an
auxiliary boiler bypass valve connected between the superheater
panels and the auxiliary boiler.
In accordance with certain embodiments, the step of connecting the
drum to the superheater panels includes connecting a plurality of
reheater panels in series between the superheater panels and a
condenser to bring the superheater panels and the reheater panels
up to an operational temperature for producing solar power. The
method can include connecting a first turbine stage in series
between the superheater panels and the reheater panels by opening a
first turbine valve connected between the superheater panels and
the first turbine stage and closing a first turbine bypass valve
connected between the superheater panels and the reheater panels,
and connecting a second turbine stage in series between the
reheater panels and the condenser by opening a second turbine valve
connected between the reheater panels and the second turbine stage
and closing a second turbine bypass valve connected between the
reheater panels and the condenser.
The step of circulating fluids through a plurality of steam
generator panels exposed to solar radiation to elevate temperatures
within the steam generator panels can include heating fluids within
the steam generator panels to a temperature within about
.+-.100.degree. F. of that within the drum. The step of circulating
fluids heated by an auxiliary boiler through an auxiliary fluid
circuit can be initiated prior to local sunrise.
The step of connecting the drum to the steam generator panels can
be timed to occur during or after local sunrise. The step of
connecting the drum to the superheater panels can include heating
the superheater panels with solar heat flux. The step of connecting
the drum to the superheater panels can be initiated after local
sunrise.
The invention also provides a method of shutting down a solar
boiler to enable subsequent rapid startup. The method includes
cooling fluids in a main fluid circuit of a solar boiler to a
temperature below operational temperature for power production,
wherein the main fluid circuit includes a plurality of solar boiler
panels and a drum. The method also includes isolating the drum from
the solar boiler panels by closing at least one drum isolation
valve in the main fluid circuit, wherein the drum is insulated to
preserve heat therein when isolated from the solar boiler
panels.
The step of cooling can include cooling fluids in the drum to a
temperature within .+-.200.degree. F. of maximum operating
temperature of an auxiliary boiler operatively connected to the
main fluid circuit to be brought selectively into fluid
communication therewith to heat portions of the main fluid circuit
during startup. The step of isolating the drum can include cooling
fluids in the solar boiler panels to around ambient temperature.
The step of cooling can be initiated prior to local sunset.
These and other features of the systems and methods of the subject
invention will become more readily apparent to those skilled in the
art from the following detailed description of the preferred
embodiments taken in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
So that those skilled in the art to which the subject invention
appertains will readily understand how to make and use the devices
and methods of the subject invention without undue experimentation,
preferred embodiments thereof will be described in detail herein
below with reference to certain figures, wherein:
FIG. 1 is a schematic view of an exemplary embodiment of a system
constructed in accordance with the present invention, showing the
main and auxiliary fluid circuits of a solar boiler in a no-flow
state such as when shut down during a night time layover;
FIG. 2 is a schematic view of the system of FIG. 1, showing the
system at a start-up stage where the drum is isolated from the main
fluid circuit and the auxiliary boiler is operating to supply steam
to the superheater and reheater via the auxiliary fluid
circuit;
FIG. 3 is a schematic view of the system of FIG. 1, showing the
system at a start-up stage where solar radiation is heating fluids
circulating in the steam generator as the auxiliary boiler
continues to supply heat to the superheater and reheater;
FIG. 4 is a schematic view of the system of FIG. 1, showing the
system at a start-up stage where a valve connecting the auxiliary
fluid circuit to the reheater inlet is closed;
FIG. 5 is a schematic view of the system of FIG. 1, showing the
system at a start-up stage where a valve connecting the auxiliary
fluid circuit upstream of the superheater is closed, and where a
valve connecting the drum to the superheater is open to supply
steam to the superheater from the steam generator via the drum;
FIG. 6 is a schematic view of the system of FIG. 1, showing the
system at a start-up stage where solar energy is applied to the
superheater and reheater panels;
FIG. 7 is a schematic view of the system of FIG. 1, showing the
system at a start-up stage where the turbine is connected to the
main fluid circuit to initiate rolling of the turbine with steam
from the drum;
FIG. 8 is a schematic view of the system of FIG. 1, showing loading
of the turbine with steam from the superheater and reheater
panels;
FIG. 9 is a schematic view of the system of FIG. 1, showing the
steam turbine accepting full steam and ramping to full load;
and
FIG. 10 is a schematic view of an exemplary solar boiler
constructed in accordance with the present invention; showing
vertically stacked walls of steam generator, superheater, and
reheater panels.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made to the drawings wherein like reference
numerals identify similar structural features or aspects of the
subject invention. For purposes of explanation and illustration,
and not limitation, a partial view of an exemplary embodiment of a
system in accordance with the invention is shown in FIG. 1 and is
designated generally by reference character 100. Other embodiments
of systems in accordance with the invention, or aspects thereof,
are provided in FIGS. 2-10, as will be described. The systems and
methods of the invention can be used to start up solar boilers,
such as after a night time layover, and shut down solar boilers,
such as to begin a night time layover.
Referring to FIG. 1, startup system 10 for a solar boiler 100 is
shown schematically with all of the lines shut off from fluid flow
as during a night time layover or inclement weather, for example.
System 10 includes a main fluid circuit 102 including a plurality
of solar boiler panels for generating power from solar energy.
Boiler 100 includes panels for a steam generator 104, superheater
106, and reheater 108 each configured to transfer solar energy into
the main fluid circuit 102. An auxiliary fluid circuit 110 is
selectively connected in fluid communication with the main fluid
circuit 102 by a plurality of valves, as will be described in
greater detail below.
With reference to FIG. 10, reheater 108, steam generator 104, and
superheater 106 are stacked and aligned as shown in FIG. 10 with
reheater 108 on the bottom, steam generator 104 in the middle, and
superheater 106 on the top. With the individual solar boiler panels
in close alignment with one another both horizontally and
vertically, the collective surfaces of the panels create four
substantially solid receiver surfaces for receiving solar radiation
from heliostats on all four sides of boiler 100. The walls can be
arranged to face North, East, South, and West, respectively, for
example, and boiler 100 can be placed on top of a central receiver
tower in a heliostat field. With such a receiver configuration, a
field of heliostats can surround boiler 100 in all compass
directions to supply radiation for heating the working fluid. Some
or all of the remaining components of system 100 can be shielded
from the heliostats within interior space 165 of solar boiler 100,
or can be located elsewhere in the solar boiler tower or on the
ground.
Referring again to FIG. 1, an auxiliary boiler 112 is operatively
connected to auxiliary fluid circuit 110. The valves connecting
auxiliary fluid circuit 110 to main fluid circuit 102 are
configured to be opened and closed to selectively place auxiliary
boiler 112 in fluid communication with portions of main fluid
circuit 102 to supply heat to the portions of main fluid circuit
102 when solar energy is low or not available, such as during a
night time layover. In accordance with certain embodiments,
auxiliary boiler 112 is a fuel fired boiler, such as liquid fuel
fired boiler, a coal fired boiler, a natural gas fired boiler,
biomass boiler, or natural gas boiler. Any other suitable type of
boiler can be used that can operate independent of the availability
of sunlight, such as an electric boiler, a nuclear boiler, or a
geothermal boiler.
Main fluid circuit 102 includes a drum 114 for separating steam
from liquid water in a saturated steam/water flow from steam
generator 104. Drum 114 is operatively connected to supply the
steam to superheater 106 for further heating. Drum isolation valve
116 is included in main fluid circuit 102 to selectively isolate
drum 114 from other portions main fluid circuit 102 to preserve
thermal energy within drum 114 during inactive periods of the solar
boiler panels, such as at night. Drum 114 is insulated to preserve
heat therein during layover periods.
A steam generator isolation valve 118 is included in main fluid
circuit 102 in an outlet of drum 114. In its open state, valve 118
connects steam generator 104 to drum 114 as solar energy heats the
steam generator panels to a temperature around that of the drum. A
drum bypass valve 119 is included, which in its closed state
cooperates with open valve 118 to connect steam generator 104 to
drum 114, and in its open state, with valve 118 also closed, allows
circulation through steam generator 104, bypassing drum 114 as
shown in FIG. 3. A valve is not needed on the inlet of drum 114 as
long as static head from drum 114 is sufficient to prevent fluids
entering into the inlet of drum 114 when valve 119 is open, valve
118 is closed, and fluids are circulating through steam generator
104 as shown in FIG. 4. A superheater isolation valve 120 is also
included, which in its open state connects auxiliary fluid circuit
110 to a portion of main fluid circuit 102 that includes
superheater 106 and reheater 108 for building temperatures therein
for full solar operation of main fluid circuit 102.
A first stage turbine bypass valve 122, in its open state, connects
superheater 106 in direct series with reheater 108. An additional
first stage turbine bypass valve 143, in its open state, connects
superheater 106 in direct series with reheater 108. The use of
valves 122 and 143 is described in greater detail below. A second
stage turbine bypass valve 124, in its open state, connects
reheater 108 to a condenser 126 in main fluid circuit 102 in
preparation for full solar operation. A first turbine valve 128, in
its open state, connects a first turbine stage 130 in series
between superheater 106 and reheater 108 when valve 122 is closed.
A second turbine valve 132 in its open state connects a second
turbine stage 134 in series between reheater panels 108 and
condenser 126 when second turbine bypass valve 124 closed.
Referring now to FIGS. 2-9, an exemplary method of starting up
system 10 to bring solar boiler 100 up to full solar operation will
now be described. In general, starting up solar boiler 100 in
accordance with the subject invention includes circulating fluids
heated by auxiliary boiler 112 through auxiliary fluid circuit 110
that includes superheater 106 and reheater 108 to elevate
temperatures within the superheater and reheater panels. Those
skilled in the art will readily appreciate that the method can be
practiced without a reheater without departing from the spirit and
scope of the invention.
Pre-warming superheater 106 and reheater 108 with auxiliary steam
from auxiliary boiler 112 reduces startup time, and allows for full
operation to commence earlier in the day compared to the startup
time required using only solar energy. Additionally, if the boiler
panels are at ambient temperature, when the heliostats resume
concentrating solar radiation onto the panels, there is sufficient
heat flux to overheat the tubes of the panels if they are not
heated up in a controlled manner. Overheating the tubes can also
lead to metal fatigue in boiler components, which can reduce the
useful life of the components. Thus the rate of heating the boiler
panels should be controlled to be fast enough to start generating
steam quickly, but slow enough to prevent damage to the system.
Thin walled components such as typical boiler tubes are less
susceptible to thermal damage, since their relatively low thermal
mass allows them to change temperature relatively quickly. It is
particularly important to control heating and cooling of
thick-walled components, including, e.g., larger headers and piping
leading to the boiler panels, as well as drum 114.
With reference to FIG. 2, valves 136, 138, 140, and 120 are opened
to bring auxiliary boiler 112 and auxiliary fluid circuit 110 into
fluid communication with main fluid circuit 102. These initial
steps of circulating fluids heated by auxiliary boiler 112 through
auxiliary fluid circuit 110 can be initiated prior to local
sunrise, since auxiliary boiler 112 does not require sunlight. At
the initial stage shown in FIG. 2, heated fluids from auxiliary
boiler 112 circulate through superheater 106 and reheater 108 to
warm the respective solar boiler panels up from ambient
temperature.
Referring now to FIG. 3, circulation pump 142 is activated to
circulate fluids through steam generator 104. After sunrise, the
heliostats can focus the available sunlight on the panels of steam
generator 104 to supply heat to steam generator 104 to elevate
temperatures therein. Optionally, it is also possible to connect
auxiliary boiler 112 to heat steam generator 104 to supply heat to
steam generator 104. When fluids within steam generator 104 are
heated to a temperature within about .+-.100.degree. F. of that
within drum 114, steam generator isolation valve 118 can be opened
and drum bypass valve 119 can be closed to begin circulating
through drum 114. During this state, superheater 106 and reheater
108 continue to receive heat from auxiliary boiler 112. When the
temperatures within superheater 106 and reheater 108 have been
sufficiently elevated, valve 140 can be closed to shut off the flow
from auxiliary boiler 112 to the inlet of reheater 108, as shown in
FIG. 4. This is a result of the fact that superheater 106 at this
stage no longer cools the fluids, e.g., auxiliary steam, enough to
require the extra heat supplied a the inlet of reheater 108 because
the components have heated up to at or near the auxiliary steam
temperature at this point. This stage occurs when the temperature
of superheater 106 reaches around 300.degree. F. to 500.degree.
F.
With reference now to FIG. 5, when temperatures in steam generator
104, superheater 106, and reheater 108 have risen sufficiently,
valve 116 can be opened, and valve 120 can be closed. This supplies
steam from steam generator 104 to the panels of superheater 106 and
brings drum 114 and superheater 106 up to an operational
temperature for producing solar power. The step of connecting drum
114 to main fluid circuit 102 puts drum 114 in series with
superheater 106 and reheater 108. At this stage, the superheater
106 and reheater 108 are warmed to at or near the same temperature
as the auxiliary steam.
Referring now to FIG. 6, at this stage, which occurs after local
sunrise, the heat for superheater 106 and reheater 108 is provided
from the solar radiation received from heliostats. Auxiliary boiler
112 is only connected to main fluid circuit 102 at this stage via
valve 138 to supply heat downstream of reheater 108. This auxiliary
boiler heat compensates for cooling that may occur in superheater
106 and reheater 108 as they are being brought up to operational
temperature, to protect downstream components from unfavorable
thermal gradients.
Referring now to FIG. 7, once temperatures in superheater 106 and
reheater 108 have risen sufficiently, and once sufficient solar
radiation is available, heliostats directing solar radiation to
superheater 106, reheater 108, and steam generator 104 supply heat
for full solar power operation. Auxiliary boiler 112 can be shut
down and auxiliary fluid circuit 110 can be disconnected from main
fluid circuit 102 by closing valve 138.
With continued reference to FIG. 7, first and second turbine stages
130, 134 can be started up as follows. Slightly opening valve 128
and throttling valve 122 rolls first turbine stage 130, bringing it
in series between superheater 106 and reheater 108. Slightly
opening valve 132 and throttling valve 124 rolls second turbine
stage 134, bringing it in series between reheater 108 and condenser
126.
With reference to FIG. 8, valve 122 is closed and flow is
transitioned through valve 143 to maintain pressure in the
superheater system. This allows main steam line 141 to receive all
of the steam generated in the steam generator panels to continue
warming up. Using valves 122 and 143 in this manner is advantageous
since the turbine components are typically located remote from the
boiler components. The distance between turbine and boiler can be,
for example, nearly 500 feet. Start up steam can be routed through
valve 122, which is proximate the boiler components, until it
reaches a temperature near that maintained over night in the main
steam line 141. When the start up steam has reached this
temperature, valve 122 can be shut off and valve 143, which is
proximate the turbine components, can be used thereafter. Valves
143 and/or 124 can be left partially open to partially bypass the
turbine as needed. Those skilled in the art will readily appreciate
that in suitable applications, for example where the turbine
components are proximate the boiler components, valve 122 can be
eliminated without departing from the spirit and scope of the
invention.
With reference to FIG. 9, valves 143 and 124 are completely closed
to allow all of the steam generated in steam generator 104 into
turbine stages 130, 134. At this stage, system 10 can ramp up to
full load and operate under full solar power.
The invention also provides a method of shutting down a solar
boiler system, e.g., system 10 with solar boiler 100, to enable
subsequent rapid startup. The method can be advantageously used,
for example, to shut down a solar boiler for a night time layover.
Shut down is initiated by cooling fluids in main fluid circuit 102
to a temperature below operational temperature for power
production. The step of cooling can be initiated prior to local
sunset as the solar radiation intensity becomes attenuated. The
cooling can also be accomplished even in strong sunlight simply by
directing sunlight from the heliostats away from the solar boiler
panels as needed. Since the boiler tubes of the panels are hotter
than the surrounding environment, the panels lose heat to the
environment by convection and radiation when the solar radiation is
withheld.
Cooling the system too rapidly can be as damaging just as can
heating it too rapidly. However, the cooling process can be
controlled by initiating the shutdown procedure before sunset,
while plenty of solar energy is still available. The boiler is
slowly ramped down in load and temperature following pre-determined
temperature change limits, which can be determined by those skilled
in the art on an application specific basis. When the boiler
reaches a minimum load and operating temperature, natural cooling
commences, which can be uncontrolled since the temperatures are
cool enough to preclude damage at this stage.
When the fluids in the drum have been cooled to a temperature
within .+-.200.degree. F. of maximum operating temperature of
auxiliary boiler 112, drum 114 is isolated from main fluid circuit
102, including the solar boiler panels, by closing drum isolation
valve 116. An exemplary maximum operating temperature for an
auxiliary boiler 112 for typical applications can range from around
300.degree. F. to 752.degree. F. Valve 118 is also closed off to
isolate drum 114 from the cooling panels of steam-generator 104. In
this manner, drum 114 is isolated from the solar boiler panels as
they continue to cool to around ambient temperature, and flow
through steam generator 104, superheater 106, and reheater 108 is
shut off. Drum 114 is thermally insulated to preserve heat therein
and to reduce the amount of heating required to restart system 10
subsequently. Additionally, the larger pipes and headers associated
with drum 114 can optionally be insulated for the same purpose.
Since drum 114 retains much of its heat, subsequent startup of
system 10 is expedited. Since drum 114 is insulated and retains
much of its heat and pressure during a layover, isolating drum 114
from the rest of main fluid circuit 102 with valves 116, 118
protects the system from large temperature differentials until the
rest of main fluid circuit 102 can be brought up in temperature to
reduce or eliminate the differential. The remaining valves can be
returned to the state shown in FIG. 1, to await startup in the
manner described above.
The methods and systems described above reduce start up time, allow
for earlier completion of start up on a daily basis, and preserve
the fatigue and creep/fatigue life of the solar boiler components.
The methods and systems also preserve the temperature to a
controlled point during overnight layover of solar boilers, or any
other time shut down is required.
If freezing layover temperatures are expected, after valves 116 and
118 are closed, superheater 106 and reheater 108 can be completely
drained and kept under vacuum during the layover to prevent
freezing therein. In order to avoid draining steam generator 104,
valve 119 can be opened and pump 142 can be activated to circulate
fluids through steam generator 104. The combination of moving water
and heat generated by pump 142 can thus be used to prevent water
freezing in steam generator 104.
The methods and systems of the present invention, as described
above and shown in the drawings, provide for systems and methods
for startup and shut down of solar boilers with superior properties
including rapid start up. While the apparatus and methods of the
subject invention have been shown and described with reference to
preferred embodiments, those skilled in the art will readily
appreciate that changes and/or modifications may be made thereto
without departing from the spirit and scope of the subject
invention.
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